The regulation of human globin gene expression is a critical problem in human hematopoiesis. An understanding of this regulation could lead to new approaches to the treatment of hereditary disorders of human hemoglobin including sickle cell anemia and the thalassemias. Recent studies indicate that multiple genetic elements within and flanking the globin genes are involved in the tissue-specific and developmental regulation of these genes. The current proposal will extend our ongoing studies of the cis acting elements within and surrounding the gamma, delta, and beta globin genes regulating the expression of these genes, and the trans acting factors in erythroid cells whose interactions with these cis acting elements are responsible for their regulated expression. More specifically, the goals of these studies are: 1) To define in more detail the cis acting elements within or surrounding the gamma, delta, and beta genes by characterizing new natural (inherited) mutations and by the in vitro construction of hybrid and mutant genes. We will continue to analyze the effect of these mutations after gene transfer into embryonic-fetal (K562), fetal-adult human (KMOE), mouse erythroleukemia (MEL), and nonerythroid cells. 2) To continue to study the role of trans acting factors in erythroid cells that regulate the expression of the epsilon, gamma, delta, and beta globin genes. In these studies, we will attempt to isolate and characterize these factors from various erythroid and nonerythroid cell lines at different stages of development. Characterization of these specific regulatory factors could lead to their cloning and to their use in stimulating gamma globin production in human erythroid cells, a potential approach to the treatment of beta thalassemia and sickle cell anemia. In addition, these experiments may increase our understanding of the processes regulating the switch from gamma globin to beta globin synthesis that occurs in late fetal life.